The present invention relates to guide means for rolling elements, as in the ball race of a travel shoe containing plural rows of balls which travel under load within a partial section thereof.
Such devices are known as "ball-race shoes" or "ball-race guides" and are used for linear bearings under high load, among other things in machine construction. They are similar to the roller-race shoe described in West German Pat. Nos. 2,121,847 and 2,264,100, with the difference that, instead of rollers, a plurality of separately guided rows of balls is employed.
Ball-race shoes have the advantage over roller-race guides, that they avoid the so-called "grinding" action of rollers, due to a sliding axial displacement of rollers with respect to their travel paths, since as a rule, rollers do not travel exactly parallel to their guided direction.
Ball-race guides cannot be subjected to as high a load as roller-race guides, in view of smaller load-bearing surfaces of balls, for the same shoe dimensions.
Both roller-race shoes and ball-race shoes present a problem which limits their use for highly precise tasks, as for example for the guidance of displaceable parts in measurement machines. This problem is manifested in a periodic run-out error (in the order of magnitude of up to several .mu.m) which is caused by the entrance of a ball or roller from the deflection region into the load region and by the associated change in loadbearing surface. This run-out error is further increased by the tendency of balls within separately guided rows to "synchronize" themselves in the course of shoe operation, i.e., for the balls of all rows to travel simultaneously in and out of the load region.
From West German Pat. No. 2,121,847 it is known, in the case of a roller-race shoe, to accommodate the transition into the load region via a resilient lug which is elastically and upwardly deflected by the incoming rollers, thus providing an entrance ramp. However, this measure only improves run-in behavior of a roller-race shoe under greater-load conditions, when substantial deflection of the lug occurs.
From West German Pat. No. 2,264,100 and West German published patent application (Offenlegungsschrift) OS 2,620,864, it is known to provide a shallow bevel at the run-in region for rollers in roller-race shoes. This bevel has the purpose of delaying the flow of rollers within the run-in region; its angle is selected correspondingly large. Therefore, the aforementioned run-out error also occurs in these known roller-race shoes.